This invention relates generally to the art of packaging films and more particularly to films useful in the packaging of food and other products.
It is common practice in packaging many goods, including food items, to use what is generally known as form-fill-seal equipment. In the vertical form-fill-seal arrangement, flexible packaging material is fed from a rollstock to a tube former where a tube is fashioned from the sheet material into a vertically dependent, upwardly open tube having overlapping longitudinal edges. These overlapping edges are subsequently sealed together longitudinally by means well known in the art and the end of the tube is sealed together by pairs of transverse heat seals which are vertically spaced apart, or closed by metal clips. At this point the tube is filled with a measured quantity of the product to be packaged. A second heat sealing or clipping operation, typically performed after the filled tube has been downwardly advanced, completes enclosure of the product. Simultaneously with or shortly after the second transverse heat sealing or clipping step the tube is completely transversely severed by known cutting means. Thereafter the tube is downwardly advanced and the cycle is successively repeated so as to form a multiplicity of individually packaged products.
Horizontal form-fill-seal equipment is also commonly used.
Manufacturers of form-fill-seal equipment include Hayssen, Omori, Ilapak, and Kartridge Pak. The latter is used to make a clipped pouch.
Flexible packaging material useful for this as well as other applications typically must meet stringent requirements imposed by the particular food or other article to be packaged. Limited oxygen transmission through the packaging material under both low and high humidity conditions is an essential feature of a packaging material for long-term storage of oxygen sensitive food products. This oxygen barrier feature should maintain the packaged food products for an extended period.
Dimensional stability of the packaging material in both low and high temperature regimes is sometimes necessary to prevent warping and distortion of the package after filling.
The flexible material must also have sufficient abuse resistance to physical and mechanical abuse imposed by the entire form-fill-seal or other packaging system.
Yet another requirement of packaging material, especially in form-fill-seal systems, is good heat sealability with respect to the longitudinal and transverse (if present) heat seals, which are sometimes subjected to loading forces from the introduced product such as food product, soon after the heat seal is formed.
Of interest is U.S. Pat. No. 4,120,716 issued to Bonet which discloses adhering printed film to a flexible film envelope by corona treating a face of the printed film and the flexible envelope, and then bringing the treated surfaces into contact with each other.
Of interest is U.S. Pat. No. 4,729,926 issued to Koteles et al which discloses a thermoplastic laminate with two substrates, one of the substrates having EVOH, and each of the substrates having an outer layer of LLDPE.
Also of interest is U.S. Pat. No. 4,724,185 issued to Shah which discloses a coextruded multilayer film with a core layer of EVOH, intermediate adhesive layers, and outer layers of a blend of LLDPE, linear medium density polyethylene, and EVA.
U.S. Pat. No. 4,457,960 issued to Newsome discloses the use of EVOH and EVOH blends in a multiple layer film. The film may be made as shrinkable film, and may be melt extruded. The outside layer of the multiple layer film may be a blend of linear low density polyethylene (LLDPE) and EVA.
U.S. Pat. No. 4,495,249 issued to Ohya et al discloses a multilayer laminate film with a core layer of a saponified copolymer of ethylene and vinyl acetate, and including two outer layers of a mixture of EVA and LLDPE. The multilayer laminate film of this reference can be made heat shrinkable and has gas barrier properties.
U.S. Pat. No. 4,764,028 issued to Wood et al discloses a hang bag with corona treated laminated surfaces.
Components such as waxes, which are put into a film to give it high slip characteristics, unfortunately also tend to inhibit the adhesion of printing ink to the film surface. They can also adversely affect the ink's behaviour by reducing its abuse resistance.
The inventors have found that the process described herein is very useful in taking advantage of the beneficial properties of high slip packaging materials, while minimizing the disadvantages relating to ink adhesion and level of abuse resistance.
It is an object of the present invention to provide a process for making a thermoplastic laminate suitable for the packaging of food and other products.
It is a further object of the present invention to provide a process for making a thermoplastic laminate useful in connection with form-fill-seal machines.
It is still another object of the present invention to provide a process for making a thermoplastic laminate which provides extended shelf life to food products.
It is also an object of the present invention to provide a process for making a printed thermoplastic laminate with good ink adhesion and abuse resistance properties.